This invention relates to a single lens reflex camera with interchangeable lenses, and more particularly to mechanism for notifying the operator, at an early stage in the picture-taking sequence of operations, that the interchangeable lens is not firmly and completely mounted or seated on the camera body.
When an interchangeable lens is placed on the camera body, it is necessary to make sure that the lens is fully and completely connected to the camera body, not only for the sake of correct optical placement but also for the sake of making sure that the lens does not accidentally drop off of the camera body, as might be the case if it is not completely seated in the proper mounting position. When pictures are to be taken under pressure of time or other conditions of stress, as for example pictures by a press or newspaper photographer, or pictures taken in the midst of a crowd which may be jostling the photographer, it is easy in the excitement or pressure of the moment to change lenses hurriedly and fail to turn the lens mount quite far enough to seat it properly and fully on the camera.
It is known in the art to provide means for blocking the camera release or trigger, when the lens is not properly seated on the camera, thus notifying the operator that something is wrong when he attempts to depress the release member or trigger in order to make the exposure. However, such an indication comes too late, in many cases. The actuation of the camera release is ordinarily the last step or last thing done, when taking a picture. By the time the photographer attempts to press the camera release and thus discovers that his lens is not properly seated, there may be insufficient time to let go the camera release, grasp the interchangeable lens mount, and do whatever is necessary to complete the proper attachment or seating of the lens, and then again put his finger on the camera release to make the exposure. If the photographer desired to take a picture of a fleeting event, the opportunity is gone forever, before correction of the lens mounting can be made.
It is therefore an important object and feature of the present invention, to notify the photographer of the incorrect mounting of the lens, at an earlier stage of the steps or sequence necessary to take the picture, so that there may still be time for corrective action if the interchangeable lens is not correctly mounted. Normally the first thing the photographer does, when deciding to take a particular picture, is to look at the viewfinder or focusing screen, to start to compose the picture. Then he is likely to adjust the focus, and select and adjust the shutter speed if the camera automatically sets the diaphragm aperture, or adjust the diaphragm aperture if the camera automatically sets the shutter speed, or adjust both of these factors if the camera is not adjusting one of them automatically. Finally, after all of these steps have been taken, the photographer presses the camera release plunger, to initiate the actual exposure cycle. As above indicated, it is often too late at this moment to take any necessary corrective action if the lens is not properly seated. Accordingly, the present invention provides mechanism for notifying the photographer of the incorrect seating of the lens, at a much earlier stage, preferably at the time he first looks at the viewfinder or focusing screen. This is done, according to the invention, by providing means for blurring or distorting the image on the focusing screen, whenever the interchangeable lens is not fully and properly seated on the camera body, so that the photographer will immediately see the conspicuously blurred or distorted image the moment he looks at the focusing screen, and thus will immediately know that the lens is not properly mounted and that corrective action must be taken. By receiving this notification early in the sequence of picture taking steps rather than late, there is increased possibility of being able to take corrective action in time to get the desired picture of some fleeting event.
Several arrangements for achieving this blurring or distortion of the image on the focusing screen will be described below.